The BCGA ( British Compressed Gas Association ) have set out the recommendations for a written scheme of examination for pressure systems in Code of Practice CP23. Each specific component on a manifold, hoses, regulators safety devices etc are listed with the recommended inspection period and the recommended guideline, i.e. examine / replace / record, depending on the item.
For most manifolds, spare parts are available. However, great care must be taken that only competent service engineers are engaged to carry out this work, as a lot of the equipment is NOT interchangeable from manifold to manifold, or even gas to gas.
It is not uncommon for manufacturers to use unique thread sizes that look similar but are NOT interchangeable. ¼” BSPT and ¼” NPT for instance will thread by hand a few turns but are not sealing properly as they are different threads. Attempts to force a joint with these generally result in joint failure.